The optical examination of skin, which is observed in possibly oblique incident light, either with the naked eye, or using a magnifying glass or microscope, or with a photographic camera, is a well-known and as such well-developed technique. For example, epiluminescence microscopy (ELM) of pigmented lesions of the skin is nowadays a well-established method for the early detection of skin cancer, also for the differential diagnosis of pigmented skin lesions.
The physical-optical principle used here is simple: The skin, or a pigmented skin lesion, is observed using a device having a 4-to 10-fold magnification, such as a magnifying glass device or an operating microscope. The observed area is illuminated by a light source which is usually directed at least substantially orthogonally onto the surface of the skin. In order to be able to make use of the effect of ELM, a plane glass surface is introduced between the magnifying glass device and the surface of the skin. A few drops of immersion fluid, usually oil, are applied between the glass surface and the skin surface. This technique reduces the amount of light diffusely reflected from the ordinarily rough skin surface, and the observer is able to see down to the boundary zone between the epidermis and dermis. The pathological process of pigmented lesions is localized at this boundary zone, the so-called dermo-epidermal junction zone, as well as in the adjacent zones, such as in the epidermis or in superficial layers of the dermis.
By using ELK, a trained dermatologist can therefore gain a more accurate view of the anatomy of pigmented lesions and thus distinguish at a much earlier date between malignant and benign lesions.
A large number of international publications confirm the beneficial effect of ELM in the early diagnosis of malignant skin melanomas.
As has been found in practice, in addition to the above-mentioned, undoubtedly positive effects, the traditional method of epiluminescence microscopy (incident light microscopy) which has just been described possesses in particular the following disadvantages:
Up until now, ELM has been carried out with hand-held magnifying glasses or operating microscopes. Documentation and discussion of the resulting images is rendered difficult as a result and requires the use of a cumbersome archiving and documentation infrastructure. PA1 By applying immersion oil to the skin and under the described glass plate, inclusions of air usually occur, and these render diagnosis more difficult. PA1 An unconventional photographic method, which itself embodies a number of disadvantages, is still used for the--understandably very important--documentation of pigmented lesions. PA1 The photographic process cannot be immediately evaluated and in addition it is always necessary to make a series of exposures. PA1 The photographic process is not standardized; mention should be made here, for example, of the variability in the film material and the variability of the wet development process, because of which the results obtained are not comparable with each other, at least as regards assessment of gray scale or color. PA1 The photographic process can only be used for comparative examinations if additional auxiliary devices such as slide projectors are employed. PA1 The task of selecting and archiving photographic materials involves a relatively high degree of effort and expense. PA1 The pigmented lesion is reliably detected as a separate entity from the surrounding skin by means of multi-phase segmentation or by local threshold value formation. A colored image is not necessary for this purpose. A black-and-white image from the red+green channel, e.g. of the video system, is sufficient. In the method used here, the image is reduced to 10 grey values, with the highest grey scale 10 representing healthy skin and the lowest grey scale 1 the darkest site on the pigment lesion. In this way a very coarse image is obtained of the lesion, although the outline of the lesion is accurate, and of the surrounding skin. It is a particular advantage of this procedure that the lighting does not have to be exactly calibrated because only relative variables are processed. PA1 In a masking step, the image-data-reduced lesion is automatically masked. PA1 Using a binary image of the total lesion, the following parameters are determined: Area, circumferential dimension, axial orientation, i.e. symmetry, fractal dimension of the boundary, also aspect ratio. PA1 The margin of the lesion is assessed as follows: Because the boundary of a pigment lesion can provide a great deal of information about the malignity of the lesion, the margin is assessed in such a manner that a binary image is produced from the grey scales 9, 8 and (8+9), and this binary image is analyzed to determine its area in relation to the total area, circumference and fractal dimension. PA1 In order to assess the color and color distribution, the image is transferred via formulae from the RGB-color region (red-green-blue) to the HSI-color region (hue-saturation-intensivity). In the HSI image, the coloration of the object is represented by a per definition black-and-white image. This image, as well as the variation in the distribution of the grey values, provide information on the variability of the coloration, PA1 The data are then evaluated via a neuronal network in the following manner: Using the method described above it is possible to significantly reduce the volume of data contained in an image; nevertheless, there are a very large number of parameters which are not available to the diagnostician for assessment because they are so numerous. A wide range of multi-variant procedures can be used for evaluation purposes in order to arrive at a sensible, informative and also sensitive classification. The most suitable method for this purpose has proved to be the use of a neuronal network which has already been confronted by several hundred training data of known diagnoses according to the pattern described below. Advantageously a so-called "back-propagation" algorithm is used. In this way, even when running on a PC, already trained networks can arrive at the appropriate diagnosis with the aid of the aforementioned data within just a few seconds. PA1 1. The Video-Blaster frame grabber under Windows. PA1 2. Mi(k)ro Movie pro frame grabber under Windows. PA1 1) patient documentation and archiving PA1 2) image documentation and archiving PA1 3) output of findings PA1 activate the image in question PA1 activate the comparison option.
Summarizing, therefore, it can be stated that the procedure currently used to examine and assess pigmented skin lesions is efficient, but suffers from many disruptive and cost-related factors.